In a multiple-stage supercharging system, a first actuating element is provided with which the charge pressure of a first exhaust gas turbocharger is set, and a second actuating element is provided with which the charge pressure of a second exhaust gas turbocharger is set.
As described, for example, in published German patent document DE 41 07 693 and published European patent document EP 04 54 943, the charge pressure regulation involves a regulator forming a controlled variable dependent on the deviation between a target charge pressure and an actual charge pressure. This controlled variable is used either to control a valve in a bypass that bridges the turbine of the charger in the exhaust gas channel, (e.g., as in published German patent document DE 41 07 693), or to control the adjustable guide vanes of a turbine having variable geometry (e.g., as in published European patent document EP 04 54 943).
Increasingly higher demands are being made on engines with respect to exhaust gas and consumption values. An exhaust gas turbocharger with variable turbine geometry enables an adaptation to the current engine operating point by adjusting the turbine guide vanes. With this technique, a delayed response of the turbocharger (turbo lag) can be reduced, while simultaneously improving the efficiency of the engine. During acceleration phases, strong overshooting of the charge pressure often occurs, which places very high mechanical stress on the turbocharger. In addition, an excessive closing of the variable turbine geometry in the acceleration phase can result in an undesirably high exhaust gas back pressure, which has a negative influence on the dynamics and efficiency of the engine.
Published German patent document DE 10 010 978 describes a device for controlling the charge pressure of an internal combustion engine having an exhaust gas turbocharger whose turbine situated in the exhaust gas channel of the internal combustion engine has a changeable geometry, the regulation of the charge pressure taking place via an adjustment of the turbine geometry. A regulator forms a controlled variable for the turbine geometry dependent on the exhaust gas back pressure prevailing in the exhaust gas channel before the turbine. In this way, the above-described problems are satisfactorily solved for the case of an internal combustion engine having single-stage supercharging.
An object of the present invention is to provide a method and a device for charge pressure regulation of an internal combustion engine having multiple-stage supercharging, the charge pressure follows the curve of the desired charge pressure target value as rapidly as possible when there is a change in load, and an overshooting of the charge pressure target value is avoided in order to protect the turbocharger from unnecessarily high stress.